Substation telephone circuit



Jul 19 1927.

y A. B. SMITH SUBSIATIQN TELEPHONE CIRCUIT Filed May 22, 1922 Inuan or EF 5 Patented July 19, 1927.

UNITED STATES DELAVJARE.

PATENT orr cg.

ARTHUR BESSEY SMITH, or nvans'ron; ILLINOIS, ASSIGNOR, BY MnsNn Assren- MENTS, TO AUTOMAT C ELECTR C Inc, or CHICAGO, I L no s, A CORPORATION or SUBSTATION TELEPHONE CIRCUIT.

Application filed May 22,

The present invention relates in general to sub-station telephone circuits, but more especlally to sub-station telephone circuits for automatic telephone systems; and the with the bell box.

A further object is to provide standard terminal and wiring arrangements in a desk telephone of the character described above whereby the circuit may be readily changed to any desired one of a plurality of other circuits.

"Having set forth the object and scope of the invention in general terms, the circuits and apparatus involved will now be ex plained more in detail, reference being had to the accompanying drawings, in which Fig. 1 is a Wiring diagram of an automatic desk telephone and bell box, Fig. 2 is a simplified circuit diagram, while Fig. 6 is a schematic diagram of the impulsing circuit.

Figs. 3, 4, and are other desk telephone circuits which may be readily produced from the circuit shown in Figs. 1 and 2, as will be described shortly in connection with Fig. 1. More particularly,

Fig. 3 is a simplified circuit diagram of an; anti-side tone desk telephone with a polar receiver. I

Fig. 4 is a simplified circuit diagram of a series type desk telephone without an induction coil and with a nonpolar receiver.

Fig. 5 is a simplified circuit diagram of a booster type desk telephone with a polar receiver. i i

Referring to Fig. 2, the talking circuit, as before stated, is of the booster type with a non-polar receiver. With the receiver re} moved from the switch-hook, the winding of the induction coil, receiver R, and transmitter T, are bridged across the two line conductors 2 and 3. 'A shunt path may also be traced around the transmitter T, which.

. path extends from the upper terminal of 1922. Serial 562,633,

. denser C will be charged due to the difference in potential across the upper and lower terminalsof the transmitter T, the amount of charge dependingon the voltage across the transmitter terminals; As the, resistance of the transmitter is increased, the main line current is reduced and the charge of the condenser is increased. WVindings 4 and 5 of the induction coil are so connectedthat the charging current induces in the primary winding 4 a current which is in opposition to the main line current, thereby further reducing it. When the resistance of the transmitter is reduced, the condenser discharges through the winding- 5 and this time induces a current in winding 4 which assists the main line current. By this arrangement the well-known booster eliect takes place.

For receiving incoming signals, the ringer M is provided, which is normally bridged across the line independent of control by the switch-hook. It will be observed that the ringer bridge includes a condenser, and that this condenser is the same one included in the shunt circuit of the transmitter.

Associated with the lower side of the line is the subs'cribersimpulse sender, or calling device,which is indicated by the reference character S. This sender may be of the type which is shown and'described on pages 34 and 35 of Automatic Telephony by Smith and Campbell, published by Mc- Graw-Hill Book Company. It comprises essentially a pair of impulse springs 15 and 16 which are controlled by a cam (not shown) through the medium of a finger hole dial (not shown), and three shunt springs j 12, 13, and 14, together with suitable means for retaining thesesprings in the position shown in the drawing when the calling de vice is not in use, and for causing'all three springs to come into engagement with each other when the calling devicedial is turned from its normal position. The impulse springs 15 and 16 are connected in series with the lower line conductor 2, andtheir function is to produce momentary. interruptions of the line circuit for the purpose of relay to bring about the operation of the operating the central otfice switches. The function of the shunt springs 12, 13, and ill is to short circuit or shunt the transmitter T and the receiver R while the calling device is being operated to send impulses. To accomplish this, spring 12 is connected to one side of the receiver, spring 13 is connected to the junction of the other side'ot the receiver and one side oi? the transmitter, while spring 14 is connected to the other side of the transmitter, and it will be evident that with the springs connected in this manner, when they are brought into engagement, the receiver and transmitter will be short circuited as stated.

. In. Fig. 1 the circuits have been drawn out in detail, corresponding parts being indicated by the same reference numera s as in Fig. 2. The apparatus at'the right of the drawing, comprising the transmitter T, the receiver R, the hook-switch H, and the calling device S, constitutes the desk telephone proper; while the apparatus to the left of the drawing, comprising the ringer M, the condenser C, and the induction coil I is separate from the telephone and in accordance with the usual practice is located in the bell boX. The telephone is provided with a terminal strip P in the base thereof, and the bell box is provided with a terminal strip P. The various circuits are completed by means of a cord which connects the two terminal strips which, it will be observed, comprises only three conductors. The line extending to the exchange is connected at the terr inal strip P as illustrated in the drawing.

The operation of the substation circuit is as 'l'ollows: lVhcn the receiver is removed to initiate a call, the swiich hook conta t springs T and 9 come into engagement with the contact springs 6 and S, iespcctivcl whereby the transmitter T is bridged across the line in series with the receiver R and the primary winding of the'induction coil, and the secondary winding is connected in shunt ot the transmiter in series with the condenser C. Responsive to the closure of the switch hook springs, current is supplied to the transmitter and receiver irom a bridge battery at the central oilice (not shown) over the following path: line conductor 3, winding 4 of the induction coil, receiver R, transmiter T, switch-hook springs 8 and 9, and the impulse springs 15 and 16 to the line conductor 2. The bridge at the central ottice, which includes the battery, may also in accordance with the usual practice include the controlling relay of an automatic switch, the circuit of the controlling relay including therefor the transmitter and receiver bridge at the telephone. It follows that by suitably manipulating the calling device dial, the calling subscriber may produce a series ot terruptions in the circuit of the control] switch.

Considering a little more closely the opcrations which take place at the telephone dur ing the transmiss' in of a series of impulses, it will be noticed that as soon as the dial is turned from its normal position, the shunt springs are closed together, anl the substation loop is completed over a path which may be traced from the line conductor 3 by way of winding; 4: of the induction coil, shunt springs l2, l3, and 14, switch-hook springs 8 and 9, and the impulse springs 15 and iii to the line conductor 2. It will be seen that the receiver and the variable resistance of the transmitter are excluded from the switch control during the entire time that the calling device is in operation, and are included again in the bridge across the line only when the calling device dial returns to its normal position. The shunting ot the receiver takes care of the usual requirement of silent operation, so that the subscriber is not annoyed by hearing clicks in the receiver caused by the interruptions oi the line circuit. Another result accomplished by the short circniting of the transmitter and re cciver is the reduction of the impedance of the shunt circuit connected around the ringer M, which includes only the windings 05 -l and 5 of the induction coil.

To continue, the first operation of the calling device brings about the operation of the first selector switch at the exchange, and succeeding operations of the callingdevice will now result in the operation oi additional switches until the connection is finally completed to the line of the called subscriber, it being understood that all of the switches are provided with controlling relay hridg which, with the exception of the bric the last switch, are successively cut oil om the line after their associated switches are operated.

The connection having been completed, conversation may be held as desired, the talkin circuits functioning the same usual in such cases. The receiver is replaced at the end of the conversation, the circuits of the transmitter and receiver are broken at the s vitc-h-hook contacts, and further flow of direct current through the substation from the exchange is prevented. As a result, all the switches used in the connection at the central oflEice are released and restored to normal in the usual manner. The substati on is now in condition to receive inconjiing signalling currents which may come in over the line conductors 2 and 3, and. pass through the r iger M and condenser C, whereby the ringer is actuated to advise the subscriber that he is being called. it is noted that with the receiver on the hook, contact springs 6 and 7 are separated and the shunt around the ringer M is broken,

The impulse transmitting circuit which, as before stated, is exceedingly efiicient and reliable is shown in schematic form in Fig. 6, which shows the conditioner the "circuit through the. substation when the dial is away from its normal; position, in other words, when the impulses are being transmitted. The essential elements are the impulse springs, the permanent bridge including the condenser andthe-ringer, and the shunt around the ringer which includes the windings 4; and 5 of the induction coil. Since all the non-essential elements, such as contact springs, etc., and the elements which are short circuited are omitted inthe schematic drawing, the relation between the parts shown may be perceived at once. It will not be necessary to go into a minute consideration of the operation of its circuit from a strictly technical standpoint, as there are a large number of different line c'ondi ti'ons which might enter into a theoretical discussion of the electrical properties of the circuit, and a thorough treatment of the subject would become exceedingly complicated. It may be stated, however, that certain amount of capacity connected in shunt of the impulse springs is an advantage under a great many line conditions, especially ii" there is a considerable amount of loop resistance. Notwithstanding this, when the condenser and ringer are permanently connected across the line in the usual manner without shunting the ringer, the condenser injuriously affects the impulses because of the exceedingly high impedance of the ringer which is in series with it, as this causes the condenser to charge and discharge very slowly. For instance, it' we consider Fig. 6 and assume that the inductioncoil windings t and 5 are omitted, when the calling device springs are closed, the condenser bridge is short circuited and the condenser will be discharged. At each interruption of the circuit, the line relayof the switch at the exchange, it it operates properly, should deenergizc at once, but with the calling device springs open the condenser bridge is left across the line, and the condenser is im inediately charged in series with the line re lay. Owing to the fact that this charging circuit also includes the high impedance ringer, the condenser will charge slowly and the resulting current flow will be prolonged appreciably, thereby causing the de-energization of the line relay to be delayed. In

other words, the effect of the condenser and ringer bridge is to make the line relay sluggish in responding to interruptions. in the line circuit.

Let us consider now the circuit with the induction coil windings present, connected as shown in Fig. 6. The benefit derived by having the inductioncoil windings connect-, ed inshunt' of ther nger while unpulsesare The impedance of the induction coil wind-' ings is almost negligible and it will be'evident, therefore, that with the circuit ofFig. 6, the condenser Wlll charge and discharge .much more rapidly, and the charging cur rent, through the line relay will not be prolonged as m. the tormer instance where the induction coil windings were not connected in shunt-oi the ringer, with the result that r the line relay is deenergized much more promptly when its circuit is interrupted.

Having described the new desk tGlQ/pllQift. a brief explanation will now be given of the manner and means by which this circuit may be conveniently changed into several other types of desk telephone circuits.

As before stated, the telephone is equippedwith a terminal strip P to which the different pieces of apparatus required to make up a complete automatic desk telephone are connected. The terminal strip P has a series of binding posts as indicated to which wires with attached terminal clips can be easily and readily connected or disconnected. The conductors of the cord leading to the bell .l)OX,.tl16 conductors of the calling device S,

the conductors of the receiver cord, and the wire X are'all equipped with such at tached terminals so that they are easily interchangeable. The other conductors are permanent, and may be soldered directly to lugs'on their respective binding posts as shown in Fig. 1.

lVith theabove arrangement ot terminals the different types of desk telephone circuits shown in Figs. 3, 4, and 5 can be readily obtained. The following code gives the changes that are necessary. a

F c'g. '5. Anti-side tone telephone circuit with polar receiocr.-Move receiver conductor from terminal 25 to terminal 27; move receiver conductor from terminal 22 to terminal 24; move wire XTirom terminal 27 to terminal 22; and change to polar receiver.

Fig. 4. Series circuit with a nowpolar re- 0cicer.0mit induction coil, and connect together terminals 34 and 36 at the terminal strip P in the bell box.

Fig. 5. Booster telephone circuit with polar recei ver.l\a[ove receiver conductor from terminal 25 to terminal 27', move wire X from terminal 27 to terminal 22; and change to polar receiver.

The circuits shown in Figs. 3,4, and 5 form no, part'of the present invention and consequentlywill not be described in detail.

Serial No. 452,467, filed March 15, 1921 that thec rcait hownin F g 3 i t e same as the lilo circuit of Fig. .Xcept that the local receiver circuit excludes the transmitter; and that the circuit shown in Fig. is substantially the same as the well known series circuit which is in common use throughout the country.

iVhile the explanation might perhaps be further amplified, it is believed that the toregoing will be sullicient to enable the invention to be understood and used by those skilled in the art. It will be seen. that l have devised an especially advantageous circuit "for an automatic desl: telephone, which includes an impulse transmitting circuit of high elliciency and which, in addition, uses a non-polar receiver and has the various parts so arranged that the minimum injunber of conductors connecting the bell box with the desk stand is maintained; while at the same time the various parts are so ranged and terminal, are provided such that different types of telephone circuits can be readily obtained by simply changing a few conductors, and without having to open or change soldered connections.

Having described the invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

l vhat I claim is:

1. In a substation telephone set, an induclion coil, a transmitter, a receiver, and one winding of said induction coil in bridge oi the line, a ringer and a condenser in a seconc bridge of the line, a local circuit connecting the two tern'linals o't said transmitter and i ncluding said condenser and the second winding of said induction coil, an impulse sender vtor producing interruptions in the said first bridge to transmit impulses over the line to the exchz'inge, the said second bridge remain ing closed meanwhile, and means tor closing a low impedance shunt circuit around the said ringer while the said sender is being operated.

2. In a substation telephone set, an induc tion coil, atransmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a sec ond bridge oi. the line, a local circuit connectiiro the two terminals of said transniitte and including said condenser and the second winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, means for closing a low impedance shunt circuit around the said ringer while the said sender being operated, and means for short-circuiting the said transmitter at the same time,

3. In a substation telephone set, an in duction coil, a transmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge of the line, a local circuit connecting the two terminals of said transmitter and including said condenser and the second winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, and means for connecting the two windings of said induction coil in parallel with the said ringer while the said sender is being operated.

4-. In a substation telephone set, an induction coil, a transmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge of the line, a local circuit connecting the two terminals of said transmitter and including said condenser and the second winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second, bridge remaining closed meanwhile, a shunt circuit around the said ringer including the two windings of said induction coil and the receiver, and contacts for short-circuiting said receiver while the said sender is being operated.

In a substation telephone set, an induction coil, a transmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a. second bridge of the line, a local circuit connecting the two terminals of said trans n'iitter and including said condenser and the second winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, and contacts actuated only during the operation of arid sender for connecting one winding of said induction coil in a shunt path around said ringer.

6. In a substation telephone set, an induction coil, a transmitter, a receiver, and one winding oi said induction coil in bridge of the line, a ringer and a condenser in a second bridge of theline, a local circuit connecting the two terminals of said transn'iitter and including said condenser and the second winding o'l said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, and contacts actuated only during the operation of said sender for short-circuiting said trans mitter. v

7. In a. substation telephone set, an induction coil, a transmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge of the line, a local circuit connecting the two terminals of said transmitter and including said condenser and the. second Winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, and contact: actuated only during the operation of said sender -tor short-circuiting said receiver.

8/111 a substation telephone set, an induction coil, a transmitter, a receiver, and one winding of said induction coil in bridge of the line, a ringer and a condenser in a second bridge 01 the line, a local circuit con necting the two terminals of said transmitter and including said condenser and the second winding of said induction coil, an impulse sender for producing interruptions in the said first bridge to transmit impulses over the line to the exchange, the said second bridge remaining closed meanwhile, and contacts actuated only during the operation of said sender for short-circuiting both the receiver and the transmitter.

9. In a substation telephone circuit, an induction coil, a transmitter, a receiver, a normally open bridge of the line including said transmitter, said receiver, and one winding of said coil, a pair of switch hook contacts for closing said bridge, a. ringer and a condenser included in a permanently closed bridge of the line, a calling device in series with one line conductor, a second pair of switch hook contacts, and a normally open shunt for said transmitter including both said pairs of switch hook contacts, said calling device, said condenser, and the other winding of the said induction coil.

10. In a telephonesubstation set, a trans-: mitter, a receiver, an lnductlon coll, a line circuit across which are bridgedsaid transmitter, receiver and one winding of said induction coil in series, a second bridge connected permanently across said line comprising a condenser and a ringer, and means comprising an impulsing device for transmitting impulses over said line circuit to the exchange, said condenser and the second winding of said induction coil forming a shunt path around said impulsing device.

11. In a substation circuit arrangement, two line conductors, a bridge across said conductors including the primary winding of an induction coil, a microphone and a telephone receiver, a normally closed bridge across said conductors including a signal and a condenser, a third bridge including .a secondary winding of said induction coil, said third bridge being connected to said second bridge at a point between said signal and said condenser, the other end of said third bridge being connected to said first bridge at a polnt between said microphone and said primary winding of said induction coil, a hookswitch serving to close said first and third bridges, an impulse sender havr ceiver inoperative, and an impulse path ex-' tending across said line conductors including a portion of said first bridge and extending through said pair of impulse springs.

12. In a substation circuit arrangement, two line conductors, a bridge across said conductors including the primary winding of an induction coil, a microphone and a telephone receiver, a normally closed bridge across said conductors including a signal and a condenser, a third bridge including a secondary winding of said induction coil, said third bridge being connected to said second bridge at a point between said signal and said condenser, the other end of said third bridge being connected to said first bridge at a point between said microphone and said primary winding of said induction coil, a hookswitch serving to close said first and third bridges, an impulse sender having a pair of impulse springs and three normally open shunt springs arranged to be closed when said impulse springs are being actuated, said shunt springs wvhen closed functioning to render said microphone and .telephone receiver inoperative, and an impulse path across said line conductors in cluding a portion of said first bridge and extending through said impulse springs and through the shunt springs.

13. In a substation circuit arrangement, an induction coil, a signal and a condenser forming one unit, a microphone, a telephone receiver, an impulse sender, and a switchhook forming a second unit, two line conductors, a bridge across said conductors including the primary winding of said induction coil, said microphone and said telephone receiver, a normally closed bridge across said conductors including said signal and said condenser, a. third bridgeincluding the sec ondary winding of an induction coil connected across said first and second bridges, said hookswitch functioning to closesaid first and third bridges, an impulse sender having a pair of impulse springs and a plurality of shunt springs arranged to be closed when said impulse sender is operated, said shunt springs when closed serving to render said microphone andsaid telephone re ceiver inoperative, an impulse circuit including a portion of said first bridge and extending through said impulse springs, the

connections for said bridges between said 

